I just discovered that if you have formatted your micro SD card without partition, r4i 3ds kept saying about «savfile not founded».
Once again, if your card is detected in FreeBSD/Linux as daX, and there’s no daXs1 and you can successfully mount daX — you need to do this:
gpart create -s MBR daX
gpart add -t fat32 daX
That’s all — you can now use your R4i just fine.